CVE-2026-55556
Description
Rsyslog is a rocket-fast system for log processing. From 8.2110.0 until 8.2604.0, the optional imhttp module's parse_auth_header function in contrib/imhttp/imhttp.c allocates a zero-byte heap buffer with calloc(0, len) when an HTTP Basic Authorization value exceeds its fixed work buffer, then passes that pointer to apr_base64_decode. An unauthenticated remote attacker can send an oversized encoded credential to an imhttp endpoint configured for Basic Authentication, causing decoded data to overwrite adjacent heap memory before credential validation. Deployments that do not install, load, and use imhttp with Basic Authentication are not affected. The demonstrated impact is a process crash that interrupts log collection, and code execution has not been demonstrated. This issue is fixed in version 8.2604.0.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
Propose a mitigation on Community Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
SUSE Affected 1 release
| Version | Status | Fixed in |
|---|---|---|
| — | Affected | — |
Debian Mixed 5 releases
| Version | Status | Fixed in |
|---|---|---|
| trixie | Affected | — |
| sid | Fixed | 8.2604.0-1 |
| forky | Fixed | 8.2604.0-1 |
| bullseye | Affected | — |
| bookworm | Affected | — |
References
- https://security-tracker.debian.org/tracker/CVE-2026-55556
- https://www.suse.com/security/cve/CVE-2026-55556.html
- https://github.com/rsyslog/rsyslog/commit/acde2ba25ea33816694b787859f4a727a247b6d6
- https://github.com/rsyslog/rsyslog/pull/6722
- https://github.com/rsyslog/rsyslog/releases/tag/v8.2604.0
- https://github.com/rsyslog/rsyslog/security/advisories/GHSA-947w-69ph-mc2r
- http://www.openwall.com/lists/oss-security/2026/06/23/4
CWEs
CWE-122
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.